Dr. Karlton Crabtree Profile

Dr. Karlton Crabtree

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Publications (10)

Proceedings Article | 6 July 2018 Open Access

Exoplanet telescope diffracted light minimized: the pinwheel-pupil solution

James Breckinridge, James Harvey, Karlton Crabtree, Tony Hull

Proceedings Volume 10698, 106981P (2018) https://doi.org/10.1117/12.2311811

KEYWORDS: Diffraction, Exoplanets, Telescopes, Space telescopes, Image segmentation, Mirrors, Stars, Diffraction gratings, Point spread functions, Light scattering

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Terrestrial exoplanets shine in light reflected from a parent star. Optical spectra are required to provide evidence of a life-supporting environment. Exoplanets are very faint and their optical spectra are contaminated by the spectrum of the parent star. High angular resolution provided by large apertures is needed to distinguish between the spectrum of the exoplanet and its star. Today, large aperture telescopes use segmented primary mirrors that employ close-packed hexagonal segments. The telescope primary mirror is periodically discontinuous with straight lines. These discontinuities scatter unwanted radiation from the much brighter parent star across the field of view to obscure the light from the very faint terrestrial exoplanet. These discontinuities, which mimic a diffraction grating, result in a non-uniform distribution of background light across the image plane. This non-uniformity masks or hides exoplanets from view, to reduce the number of exoplanets that can be observed with a large aperture telescope or to reduce the quality of spectra and thus lead to misinterpretation of data. Here we introduce the concept of the pinwheel pupil whose unique diffraction pattern significantly reduces the non-uniform distribution of background radiation. Diffraction patterns from pinwheel pupils are compared to the monolithic filled aperture, the classical Cassegrain, the 60-degree symmetry of the hexagonal segments (JWST, E-ELT, etc.). Diffraction “spikes” are reduced by at least 10⁵. We discuss the “pinwheel pupil” advantages to spectroscopy, image processing, and observatory operations. We show that, segment fabrication of curved-sided mirrors is not more difficult than fabrication of hexagonal mirror segments. . This is the report of quantitative study of Fraunhofer (far field) diffraction patterns produced by three different topologies or architectures of mirror segmentation, when illuminated by a plane wave of monochromatic white-light. A plot, in angular units of the intensity as a function of azimuth, Phi_f , within annular rings at different FOVs, centered on the system axis of the diffraction pattern will be presented. The advantages of the segmented pinwheel pupil is discussed.

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Proceedings Article | 6 July 2018 Open Access

Diffraction analysis of large segmented mirror concepts for exoplanet exploration

James Harvey, Ryan Irvin, Karlton Crabtree, Richard Pfisterer, James Breckinridge

Proceedings Volume 10698, 106981Q (2018) https://doi.org/10.1117/12.2313999

KEYWORDS: Diffraction, Mirrors, Point spread functions, Segmented mirrors, Telescopes, Exoplanets, Space telescopes, Image segmentation, Image quality, Exoplanetary science

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Proceedings Article | 5 June 2018 Paper

Optical and mechanical designs of the multi-band SWIR receiver for the Lunar Flashlight CubeSat mission

Quentin Vinckier, Karlton Crabtree, Megan Gibson, Christopher Smith, Udo Wehmeier, Paul Hayne, R. Glenn Sellar

Proceedings Volume 10690, 106901I (2018) https://doi.org/10.1117/12.2302914

KEYWORDS: Receivers, Reflectometry, Short wave infrared radiation, Reflectivity, Optical design, Mechanical engineering, Radiometry

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Proceedings Article | 30 August 2017 Paper

Design and characterization of a low cost CubeSat multi-band optical receiver to map water ice on the lunar surface for the Lunar Flashlight mission

Quentin Vinckier, Karlton Crabtree, Christopher Paine, Paul Hayne, Glenn Sellar

Proceedings Volume 10403, 104030R (2017) https://doi.org/10.1117/12.2274203

KEYWORDS: Receivers, Reflectometry, Sensors, Remote sensing, Near infrared, Optical testing, Aluminum, Mirrors, Signal detection

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Proceedings Article | 27 September 2013 Paper

Airborne multiangle spectropolarimetric imager (AirMSPI) observations over California during NASA's polarimeter definition experiment (PODEX)

David Diner, Michael Garay, Olga Kalashnikova, Brian Rheingans, Sven Geier, Michael Bull, Veljko Jovanovic, Feng Xu, Carol Bruegge, Ab Davis, Karlton Crabtree, Russell Chipman

Proceedings Volume 8873, 88730B (2013) https://doi.org/10.1117/12.2024605

KEYWORDS: Clouds, Polarization, Data acquisition, Polarimetry, Scattering, Imaging systems, Aerosols, Cameras, Sensors, Data modeling

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Proceedings Article | 9 September 2010 Paper

Three-dimensional polarization ray tracing and diattenuation calculation

Garam Yun, Karlton Crabtree, Russell Chipman

Proceedings Volume 7652, 76521X (2010) https://doi.org/10.1117/12.868546

KEYWORDS: Polarization, Ray tracing, Matrices, Interfaces, Optical design, Jones vectors, Jones matrices, Polarizers, Refraction, Geometrical optics

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Proceedings Article | 21 August 2009 Paper

Illumination system design in a project-based course

R. John Koshel, Vineeth Abraham, Joshua Kim, Ron Liu, Scott Richardson, Soha Namnabat, Amber Czajkowski, Rania Abd El-Maksoud, Ryan Irvin, Takeshi Nakazawa, Michael Kudenov, Martha Dawsey, Erich de Leon, Lirong Wang, Karlton Crabtree, R. Orr, Brian Primeau, Yullin Kim

Proceedings Volume 7423, 742305 (2009) https://doi.org/10.1117/12.828806

KEYWORDS: Illumination engineering, Light emitting diodes, Systems modeling, Nonimaging optics, Reflectors, Optical design, Tolerancing, RGB color model, Light sources and illumination, LCDs

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Proceedings Article | 13 September 2007 Paper

Properties of the polarization ray tracing matrix

Garam Yun, Karlton Crabtree, Russell Chipman

Proceedings Volume 6682, 66820Z (2007) https://doi.org/10.1117/12.734315

KEYWORDS: Polarization, Ray tracing, Matrices, Transmittance, Wave plates, Reflection, Refraction, Mirrors, Jones matrices, Jones vectors

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Proceedings Article | 12 July 2006 Paper

Sub-wavelength grating induced wavefront aberrations: a case study

Karlton Crabtree, Russell Chipman

Proceedings Volume 6342, 63420C (2006) https://doi.org/10.1117/12.692200

KEYWORDS: Wavefront aberrations, Polarization, Monochromatic aberrations, Wavefronts, Transmittance, Antireflective coatings, Diffraction gratings, Thin films, Interfaces, Dielectric polarization

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Proceedings Article | 18 August 2005 Paper

Off-resonance properties of a photoelastic modulator

Karlton Crabtree, Neil Beaudry, Russell Chipman

Proceedings Volume 5888, 58880A (2005) https://doi.org/10.1117/12.621527

KEYWORDS: Modulators, Modulation, Polarization, Photoelastic modulators, Resonators, Sensors, Polarizers, Polarimetry, Phase shift keying, Acoustics

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Showing 5 of 10 publications

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